Cryoablation method and system

ABSTRACT

A system and method for providing greater control over the temperature of a thermal treatment element of a medical device, enabling an operator to extend a thawing period of a cryoablation procedure. The system may include a fluid flow path that bypasses a subcooler, giving the operator selective control over the temperature of refrigerant delivered to the treatment element and, therefore, treatment element temperature. Additionally or alternatively, the system may include a fluid delivery conduit that is in communication with a liquid refrigerant and a gaseous refrigerant. Adjustment of the ratio of liquid to gaseous refrigerant also offers control over the treatment element temperature. Additionally or alternatively, the system may include one or more valves and/or heating elements in the fluid delivery and recovery conduits to control the treatment element temperature.

CROSS-REFERENCE TO RELATED APPLICATION

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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FIELD OF THE INVENTION

The present invention relates to a method and system for providinggreater control over the temperature of a thermal treatment element of amedical device, enabling an operator to extend a thawing period of acryoablation procedure.

BACKGROUND OF THE INVENTION

Methods of thermally treating tissue are frequently used for a widevariety of medical purposes. For example, cryoablation, by which tissuemay be destroyed, may be used to treat cardiac arrhythmia, to ablatetumors in the treatment of cancer, and for dermatological and obstetricprocedures. Further, cooling tissue to sub-lethal temperatures iscommonly used in electrophysiology studies.

Regardless of the tissue being treated, the permanency of the lesioncreated by a cryoablation procedure is of the utmost importance. Thetarget tissue must be completely and permanently affected, whichprevents the recurrence of the condition being treated. In the treatmentof certain forms of arrhythmia, including atrial fibrillation (AF),permanent electrical conduction blocks must be created at specificlocations in the heart. Therefore, continuous, transmural lesions mustbe created, ensuring that all myocardial cells in the target tissue aredestroyed. Specifically, myocytes are killed acutely by cold-inducedinjury through several mechanisms that can include cell membrane rupturedue to ice formation, osmotic imbalance, dehydration, damage to themitochondria, and delayed apoptotic processes.

The type and severity of the damage to tissue cells is influenced byseveral parameters of the treatment process. In a cryoablationprocedure, for example, these parameters may include duration of thefreeze, treatment temperature, cooling and thawing rate, and the numberof freeze-thaw-freeze cycles. In fact, extending the thawing phase of acryoablation procedure by creating a temperature plateau at a mildlycold temperature, between approximately −20° C. and approximately −25°C., may result in more complete cell destruction and, therefore, areduced likelihood of reconduction. Additionally, maintaining thetreatment element in this temperature range may reduce the occurrence ofcollateral damage by preventing the freeze zone from penetrating toodeeply within the tissue.

Current cardiac cryoablation systems operate at a controlled refrigerantflow to the treatment device, resulting in an operating temperature thatis the lowest achievable in the given conditions. That is, the operatordoes not have the means to control the minimum temperature or thecooling and thawing rates. The only parameters that can be controlledare the duration of the freeze and the number of freeze-thaw-freezecycles.

It is therefore desirable to provide a method and system by whichparameters of a cryoablation procedure may be fully controllable. Forexample, it is desirable to provide a method and system by whichduration of the freeze, treatment temperature, cooling and thawingrates, and the number of freeze-thaw-freeze cycles may be controlled bythe operator.

SUMMARY OF THE INVENTION

The present invention advantageously provides a method and system forproviding greater control over the temperature of a thermal treatmentelement of a medical device, enabling an operator to extend a thawingperiod of a cryoablation procedure. In one embodiment, a system forcontrollable adjustment of the temperature of a treatment element of amedical device may include a fluid delivery conduit including anupstream portion and a downstream portion, a subcooler located betweenthe upstream fluid flow path and the downstream fluid flow path, abypass fluid flow path having a first end that is in directcommunication with the upstream fluid flow path and a second end that isin direct communication with the downstream fluid flow path, a firstvalve located in the upstream fluid flow path between the subcooler andthe first end of the bypass fluid flow path, and a second valve locatedin the bypass fluid flow path. The system may further include arefrigerant source in fluid communication with the fluid deliveryconduit. As an example, the treatment element may reach a minimumtreatment temperature when the first valve is completely open and thesecond valve is completely closed, and may reach a maximum treatmenttemperature when the first valve is completely closed and the secondvalve is completely open. The refrigerant source may be a liquidrefrigerant source, and the system may further include a gaseousrefrigerant source in fluid communication with the fluid deliveryconduit. Adjusting the ratio of gaseous refrigerant to liquidrefrigerant may selectively control the temperature of the treatmentelement. The liquid refrigerant source may be a first tank and thegaseous refrigerant source may be a second tank. Alternatively, theliquid refrigerant source and the gaseous refrigerant source may be acommon tank (that is, both liquid refrigerant source and gaseousrefrigerant source may be located in the same tank). The common tank maydefine a fluid reservoir, the liquid refrigerant source being at thebottom of the fluid reservoir and the gaseous refrigerant source beingat the top of the fluid reservoir. Further, the common tank may includea first valve in fluid communication with the liquid refrigerant sourceand a second valve in fluid communication with the gaseous refrigerantsource, manipulation of at least one of the first and second valvesadjusting the ratio of gaseous refrigerant to liquid refrigerant. Forexample, at least one of the first and second valves may be manipulateduntil the treatment element achieves a temperature of betweenapproximately −20° C. and approximately −25° C. The tank may furtherinclude a dip tube in communication with the first valve and extendinginto the liquid refrigerant source. The first and second valves may beon the same end of the common tank, or they may be on opposite ends ofthe common tank. The fluid delivery conduit may be in fluidcommunication with the treatment element, and the system may furtherinclude a fluid recovery conduit in fluid communication with thetreatment element, a first valve in the fluid recovery conduit, and asecond valve in the fluid delivery conduit, independent manipulation ofat least one of the first and second valves selectively controlling thetemperature of the treatment element. Alternatively, the system mayinclude only a valve in the fluid recovery conduit, manipulation of thevalve selectively controlling the temperature of the treatment element.

A system for adjusting a treatment temperature of a cryoablation devicemay include a refrigerant source, a fluid delivery conduit configured tobe in fluid communication with the refrigerant source and thecryoablation device, a fluid recovery conduit configured to be in fluidcommunication with the cryoablation device, and a heating element inthermal exchange with the fluid delivery conduit. The heating elementmay be a thermoelectric heater. Additionally or alternatively, the fluidrecovery conduit may include a heating fluid flow path, at least aportion of the heating fluid flow path being in thermal exchange withthe fluid delivery conduit. The heating fluid flow path may include avalve, manipulation of the valve selectively affecting the temperatureof at least a portion of the cryoablation device.

A system for adjusting a treatment temperature of a treatment element ofa cryoablation device may include: a fluid delivery conduit including anupstream portion and a downstream portion, the upstream portion being influid communication with a refrigerant reservoir and the downstreamportion being in fluid communication with the treatment element; asubcooler located between the upstream fluid flow path and thedownstream fluid flow path; a bypass fluid flow path having a first endthat is in direct communication with the upstream fluid flow path and asecond end that is in direct communication with the downstream fluidflow path; a first valve located in the upstream fluid flow path betweenthe subcooler and the first end of the bypass fluid flow path; and asecond valve located in the bypass fluid flow path, the refrigerantreservoir containing both a refrigerant in a gaseous state and arefrigerant in a liquid state, the refrigerant reservoir having a thirdvalve for delivering the gaseous state refrigerant to the fluid deliveryconduit and a fourth valve for delivering the liquid state refrigerantto the fluid delivery conduit, independent manipulation of at least oneof the first, second, third, and fourth valves controlling thetemperature of the treatment element. At least one of the first, second,third, and fourth valves may be manipulated so that the treatmentelement achieves a temperature of between approximately −20° C. andapproximately −25° C.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 shows an exemplary cryoablation system including a treatmentdevice having a treatment element;

FIG. 2 shows a first schematic diagram of a system providing fullycontrollable cryoablation parameters;

FIG. 3 shows a second schematic diagram of a system providing fullycontrollable cryoablation parameters;

FIG. 4 shows a third schematic diagram of a system providing fullycontrollable cryoablation parameters;

FIG. 5 shows a fourth schematic diagram of a system providing fullycontrollable cryoablation parameters;

FIG. 6A shows a fifth schematic diagram of a system providing fullycontrollable cryoablation parameters;

FIG. 6B shows a sixth schematic diagram of a system providing fullycontrollable cryoablation parameters; and

FIG. 7A shows a seventh schematic diagram of a system providing fullycontrollable cryoablation parameters.

DETAILED DESCRIPTION OF THE INVENTION

The present invention advantageously provides a method and system bywhich parameters of a cryoablation procedure may be fully controllable.For example, the duration of the freeze, treatment temperature, coolingand thawing rates, and the number of freeze-thaw-freeze cycles may befully controllable by the operator. Referring now to the drawing figuresin which like reference designations refer to like elements, anexemplary embodiment of a cryoablation system including a treatmentdevice having a treatment element in accordance with principles of thepresent invention is shown in FIG. 1 and generally designated as “10.”The system 10 may generally include a treatment device 12, which may bereferred to herein as a catheter, that may be coupled to a control unitor operating console 14. The catheter 12 may be configured to interactwith tissue, such as with a treatment element 16. Further, the catheter12 may include one or more electrodes with mapping and/or ablationfunctionality (not shown).

The catheter 12 may include an elongate body 18 passable through apatient's vasculature and/or proximate to a tissue region for diagnosisor treatment. The elongate body 18 may define a proximal portion 20 anda distal portion 22, and may further include one or more lumens disposedwithin the elongate body 18 thereby providing mechanical, electrical,and/or fluid communication between the proximal portion of the elongatebody 18 and the distal portion of the elongate body 18. For example, themedical device 12 may further include a fluid delivery conduit 30traversing at least a portion of the elongate body 18 and towards thedistal portion 22. The delivery conduit 30 may be coupled to orotherwise extend from the distal portion 22 of the elongate body 18 intothe treatment element 16. Although the treatment element 16 is shown inFIG. 1 as a balloon, it will be understood that the treatment element 16may be any treatment element through which refrigerant may flow and thatis capable of thermally affecting tissue.

One or more fluid injection elements 32 in fluid communication with thefluid delivery conduit 30 may be disposed within the interior chamber 34of the balloon 16. The fluid injection element 32 may be of anyconfiguration suitable for delivering refrigerant or other fluid fromthe fluid delivery conduit 30 into the balloon 16. As a non-limitingexample, a fluid injection element 32 may include a plurality ofwindings about a shaft or actuation element 36 within the chamber 34 (asshown in FIG. 1). Further, the fluid injection element 32 may includeone or more openings or ports therein to provide for the delivery and,optionally, directed ejection of fluid from the fluid delivery conduit30 to the chamber 34 of the balloon 16.

The system 10 may also include one or more fluid supply reservoirs 44,such as pressurized tanks, that include a coolant, cryogenicrefrigerant, or the like in fluid communication with the fluid deliveryconduit 30 and fluid injection element 32. As a non-limiting example, afluid supply reservoir 44 may be a refrigerant tank as shown anddescribed in more detail below. The system 10 may also include anexhaust or scavenging system for recovering or venting expendedrefrigerant for re-use or disposal. The scavenging system may include afluid recovery conduit 48 defining a passage for the recovery ofexpanded refrigerant, a fluid recovery reservoir 50, and a vacuum pump52 for creating a pressure gradient to draw expanded refrigerant fromthe balloon chamber 34 into the fluid recovery conduit 48 and then intothe fluid recovery reservoir 50 (that is, from the distal portion of thedevice to the proximal portion of the device and into the operatingconsole). The system's fluid flow path may include at least the fluiddelivery conduit 30 and the fluid recovery conduit 48, in addition tovarious other conduits and/or secondary flow paths. Further, althoughthe fluid supply reservoir 44 and the fluid recovery reservoir 50 eachmay each located within or external to operating console 14, they arereferred to as being part of the operating console 14 for simplicity.The operating console 14 may also include pumps, valves, controllers orthe like to recover and/or re-circulate fluid delivered to the handle,the elongate body, and/or the fluid pathways of the catheter 12, asdescribed in more detail below.

The operating console 14 may include one or more controllers,processors, and/or software modules containing instructions oralgorithms to provide for the automated operation and performance of thefeatures, sequences, or procedures described herein. For example, theoperating console 14 may include one or more computers 56 that includeone or more processors 58 for receiving signals from one or more sensorsthroughout the system 10, and or for the automatic, semi-automatic,and/or manual operation of the system 10. The one or more computers 56may include one or more user input devices 60 by which a user canprogram system parameters such as the inflation and deflation of theballoon 16, circulation of refrigerant through the fluid delivery andrecovery conduits, and/or the operation of one or more electrodes orother thermal delivery elements. The user input devices 60 may includekeyboards, knobs, buttons, dials, foot pedals, mice, touchscreens, voiceinput units, and/or switches. Additionally, the user may use the userinput devices to override the automatic operation of the system 10either programmed into or predetermined by the operating console 14.Still further, signals received by the one or more processors 58 may beused to automatically or semi-automatically control the configuration ofthe balloon 16 (for example, by extending or retracting the actuationelement 36). The one or more computers 56 may further includes one ormore displays 62, such as computer screens or other visual elements incommunication with the one or more processors 58 and/or user inputdevices 60. Finally, the operating console 14 may include one or morespeakers or other audio alert generators that are in communication withthe one or more processors 58 and/or the user input devices 60.

The catheter 12 may include a handle 68 coupled to the proximal portion20 of the elongate body 18. The handle 68 can include circuitry foridentification and/or use in controlling of the catheter 12 or anothercomponent of the system 10. For example, the handle 68 may include oneor more sensors to monitor system parameters such as the fluid pressurewithin the catheter 12 or one or more fluid flow paths of the system.Additionally, the handle 68 may also include connectors 72 that arematable directly to a fluid supply/exhaust and operating console 14 orindirectly by way of one or more umbilicals. The handle 68 may furtherinclude blood detection circuitry in fluid and/or optical communicationwith the injection, exhaust and/or interstitial lumens. The handle 68may also include a pressure relief valve in fluid communication with thefluid delivery conduit 30 and/or exhaust lumen to automatically openunder a predetermined threshold value in the event that value isexceeded.

The handle 68 may also include one or more actuation or control featuresthat allow a user to control, deflect, steer, or otherwise manipulate adistal portion of the medical device from the proximal portion of themedical device. For example, the handle 68 may include one or morecomponents such as a lever or knob 74 for manipulating the elongate body18, shaft 36, a guidewire, and/or additional components of the catheter12.

The system 10 may further include one or more sensors 76 to monitor theoperating parameters throughout the system 10, including for example,pressure, temperature, flow rates, volume, or the like in the operatingconsole 14 and/or the catheter 12, in addition to monitoring, recordingor otherwise conveying measurements or conditions within the catheter 12or the ambient environment at the distal portion of the catheter 12. Thesensor(s) 76 may be in communication with the operating console 14 forinitiating or triggering one or more alerts or therapeutic deliverymodifications during operation of the medical device 12. One or morevalves, controllers, or the like may be in communication with thesensor(s) to provide for the controlled dispersion or circulation offluid through the lumens/fluid paths of the catheter 12 and system 10.Such valves, controllers, or the like may be located in a portion of themedical device 12 and/or in the operating console 14.

While the medical device 12 may be in fluid communication with a fluidsource to cryogenically treat selected tissue, it is also contemplatedthat the medical device 12 may additionally include one or moreelectrically conductive portions or electrodes thereon coupled to aradiofrequency generator or power source 80 as a treatment or diagnosticmechanism. If the catheter 12 includes thermoelectric cooling elementsor electrodes capable of transmitting radiofrequency (RF), ultrasound,microwave, electroporation energy, or the like, the elongate body 18 mayinclude a lumen in electrical communication with a power source 80.

Referring now to FIGS. 2-5, schematic diagrams of a system providingfully controllable cryoablation parameters are shown. As discussedabove, the system fluid flow path may include one or more valves,conduits, secondary flow paths, one or more fluid supply reservoirs 44,one or more fluid recovery reservoirs 50, a vacuum pump 52, and othersystem components. The system 10 may also include one or more subcoolers82 with various refrigeration components such as a compressor,condenser, capillary tube, thermoelectric elements, and/or heatexchanger. Currently known cryoablation systems frequently includesubcoolers to ensure that the refrigerant is delivered to the balloon ina fully liquid state, because the refrigerant has maximum refrigerationpotential (maximum enthalpy). For example, a liquid refrigerantdelivered to the balloon 16 may cause the balloon 16 to reach atemperature of approximately −80° C. However, a system that alwaysdelivers liquid refrigerant to the balloon at maximum refrigerationpotential does not offer a means to control or adjust the temperature ofthe balloon and, therefore, to extend the thawing phase by creating atemperature plateau in the range of between approximately −20° C. andapproximately −25° C. (referred to herein as the “plateau temperature”).The thawing period may be maintained for between approximately 2 secondsto approximately 40 seconds. For example, the thawing period may bemaintained for approximately 20 seconds to achieve the desired result.

One means for providing a controllable balloon temperature is shown inFIG. 2. The system 10 shown in FIG. 2 may include a heat exchangerbypass flow path 88 that allows coolant to be delivered to the balloon16 while completely or partially avoiding the subcooler 82. The system10 may include a solenoid valve S1 that is upstream of the subcooler 82(that is, between the subcooler 82 and the refrigerant supply reservoir44) and a bypass flow path 88, the bypass flow path 88 having a firstend that is located upstream of valve S1, a second end that is locateddownstream of the subcooler 82, and a solenoid valve SX located betweenthe first end and the second end. For example, directing refrigerantthrough the bypass flow path 88 may avoid the subcooler 82 altogether.Valves S1 and/or SX may be opened or closed to modify the temperature ofthe balloon 16. Current cryoablation systems may be retrofitted with abypass flow path 88 (which may include, for example, a conduit and oneor more valves) to add temperature adjustment functionality to existingsystems. Refrigerant that passes through a subcooler may exist at atemperature below its normal saturation temperature or boiling point.Thus, the refrigerant may be in a fully liquid state upon exiting thesubcooler. If valve SX is closed and valve S1 is open, the refrigerantwill pass from the fluid supply reservoir 44 and through the subcooler82. Liquid refrigerant may then pass from the subcooler into the balloonchamber 34 via the fluid delivery conduit 30, the refrigerant being in afully liquid state. As the refrigerant exits the higher-pressureenvironment of the fluid delivery conduit 30 and fluid injection element32 and into the lower-pressure balloon chamber 34, the refrigerant willexpand into a gas (or, if delivered in a gaseous state, the refrigerantwill simply expand and remain in the gaseous state) and the temperatureof the refrigerant will decrease by the Joule-Thomson effect. Thisdecrease in temperature within the chamber 34 allows the balloon 16 toremove heat from surrounding tissue, which may result in cryoablation ofthe tissue.

If, on the other hand, a warmer refrigerant (and, therefore, balloon 16)temperature is desired, operation of the subcooler 82 may be duty cycledso that when the subcooler 82 is “on” (that is, for example, heatexchange is allowed to occur within the subcooler 82, such as byactivating a thermoelectric device or allowing heat exchange between therefrigerant and a secondary cooled liquid) the refrigerant enters theballoon 16 in a liquid state. Conversely, when the subcooler 82 is “off”(that is, for example, heat exchange does not occur within the subcooler82, such as by deactivating a thermoelectric device or preventing heatexchange between the refrigerant and a secondary cooled liquid), atleast a portion of the refrigerant may be delivered to the balloon 16 ina gaseous state. So, some portion of the refrigerant may be in a liquidstate and some portion of the refrigerant may be in a gaseous state,with the gaseous refrigerant causing the balloon 16 to reachtemperatures greater than it would if the refrigerant were delivered ina fully liquid state. This is because the gaseous portion of therefrigerant does not expand to create a lower temperature within thechamber 34.

Although duty cycling the subcooler 82 may be effective in producing awarmer balloon temperature, the temperature-modifying effects may not beinstantaneous because adjusting subcooler parameters may produce adelayed effect on the temperature of the refrigerant passingtherethrough. When immediate or substantially immediate temperatureadjustment is desired, solenoid valve S1 may be closed while solenoidvalve SX may be open, causing the refrigerant to flow through thesubcooler bypass flow path 88. Bypassing the subcooler 82 may mean thatthe refrigerant does not become fully liquefied and at least a portionof the refrigerant remains in the gaseous state.

Another means for providing a controllable balloon temperature is shownin FIGS. 3-5. Like the system 10 in FIG. 2, the system 10 in FIGS. 3-5may also include a subcooler bypass flow path 88. Thus, these systemsmay be operated similarly to the system of FIG. 2. However, unlikesystems that include a fluid supply of liquid refrigerant only, thesystems in FIGS. 3-5 may include a source of liquid refrigerant and asource of gaseous refrigerant. For example, each refrigerant source maybe an individual tank. Thus, the temperature of the balloon 16 may beadjusted by the delivery of a mixture of liquid and gaseous refrigerant,the mixture being controlled at the refrigerant source instead of byadjusting, for example, subcooler operation. However, it will beunderstood that a controlled mixture of gaseous and liquid refrigerantmay also be delivered to the subcooler 82 in cases where the subcoolerincludes a secondary refrigerant in thermal exchange with therefrigerant being delivered to the balloon 16. That is, the coolingeffect of the subcooler on the refrigerant being delivered to theballoon 16 may be determined by the temperature of the secondary coolantwithin, which, in turn, may be determined by the ratio of gaseous toliquid refrigerant. It further will be understood that the balloon 16temperature may be adjusted both by the method shown and described inFIG. 2 and by the method shown and described in FIGS. 3-5. As shown inFIG. 3, the system 10 may include a liquid refrigerant supply reservoir44 and a separate gaseous refrigerant supply reservoir 94, both of whichbeing in fluid communication with the system flow path 96 and theballoon chamber 34. The gaseous refrigerant supply reservoir 94 may alsobe added to existing systems. The delivery rate of the liquidrefrigerant from the liquid refrigerant supply reservoir 44 may becontrolled via valve 120, and the delivery rate of the gaseousrefrigerant from the gaseous refrigerant supply reservoir 94 may becontrolled via valve 122. Thus, the mixture or ratio of gaseous toliquid refrigerant may be controlled by the independent and selectivemanipulation of valve 120 and/or valve 122.

Alternatively, as shown in FIG. 4, the fluid refrigerant supply and thegaseous refrigerant supply may be housed in a common reservoir or tank104. The common reservoir 104 may include liquid refrigerant 106 at thebottom 108 of the reservoir 104 and gaseous refrigerant 110 at the top112 of the reservoir 104, as the denser liquid may settle to the bottomof the reservoir 104. As used herein, the term “bottom” may refer to anyportion of the reservoir 104 to which gravity causes the liquidrefrigerant 106 to settle. As used herein, the term “top” may refer tothe portion of the reservoir 104 that is vertically aligned with andopposite to the bottom. The reservoir 104 may include a dip stick 114 incommunication with a first valve 120 for drawing and delivering liquidrefrigerant 106 from the bottom 108 of the reservoir 104 and into theballoon 16. The reservoir 104 may further include a second valve 122 fordrawing and delivering gaseous refrigerant 110 from the top 112 of thereservoir 104. Thus, the first 120 and second 122 valves may both belocated on the same end of the reservoir 104. The mixture of the liquid106 and gaseous 110 refrigerants delivered to the balloon 16 may beadjusted by independently and selectively adjusting valves 120 and 122between a closed position and a fully open position.

Alternatively, as shown in FIG. 5, the common reservoir 104 may includea first valve 120 at the bottom 108 of the reservoir 104 for adjustingthe flow of liquid refrigerant 106 and a second valve 122 at the top 112of the reservoir 104 for adjusting the flow of gaseous refrigerant 110.The liquid refrigerant 106 may be at the bottom 108 of the reservoir 104and the gaseous refrigerant 110 may be at the top 112, as shown anddescribed in FIG. 4, and therefore the liquid refrigerant 106 may bedrawn from the first valve 120 at the bottom 108 whereas the gaseousrefrigerant 110 may be drawn from the second valve 122 at the top 112.Like the system of FIG. 4, the mixture of the liquid 106 and gaseous 110refrigerant delivered to the balloon 16 may be adjusted by independentlyand selectively adjusting valves 120 and 122 between a closed positionand a fully open position. The common reservoir 104 as shown in eitherFIG. 4 or FIG. 5 may be added to existing systems.

Another means for providing a controllable balloon temperature is shownin FIGS. 6A and 6B. The system in FIGS. 6A and 6B may include one ormore heating mechanisms. For example, the heating mechanism may includea heat exchange flow path 126 that includes an area 128 at which thedelivery conduit 30 and the recovery conduit 48 may be in thermalexchange with one another (as shown in FIG. 6A). Solenoid valve 138 maybe selectively opened or closed to allow warmer fluid in the recoveryconduit 48 to be in thermal exchange with the refrigerant in thedelivery conduit 30 via heat exchange flow path 126. As a result, thetemperature of the refrigerant in the delivery conduit 30 may beincreased.

Additionally or alternatively, the system 10 may include one or morethermoelectric heating elements 130 distributed at any point(s) in thesystem flow path 96 between the operating console 14 and the catheter 12on the fluid delivery side (as shown in FIG. 6B). Generally,thermoelectric heating elements 130 would not be located within thecatheter 12 in order to avoid the need to send additional power into thecatheter 12.

Another means for providing a controllable balloon temperature is shownin FIG. 7. Like the systems shown and described in FIGS. 2-6, the system10 of FIG. 7 may also include a subcooler bypass flow path 88. Thesystem 10 in FIG. 7 may also include a proportional valve 136 in thefluid recovery conduit 48 that may be adjusted to create a restrictionin the fluid recovery conduit 48. This restriction may slow refrigerantflow rate from the balloon chamber 34 into the fluid recovery conduit48, thereby increasing the pressure within the balloon chamber 34. Thepressure increase within the chamber 34 may cause an increase in theboiling point of the refrigerant therein. As a result, the refrigerantwithin the chamber 34, and thus the balloon 16, may have a warmertemperature than if the refrigerant were allowed to freely flow from thechamber 34 into the fluid recovery conduit 48. Adjusting the valve 136between the closed position and the fully open position may thereforeallow the operator to control the temperature of the balloon 16. Forexample, the balloon temperature may be lower when the valve 136 isfully open than when the valve 136 is fully or substantially closed.

Similarly, proportional valve MKS in the fluid delivery conduit 30 andvalve 136 in the fluid recovery conduit 48 may be individually andselectively controlled, either sequentially or simultaneously, to adjustthe temperature of the balloon 16. For example, fully or substantiallyclosing valve 136 and/or fully or substantially closing valve 136 mayproduce a warmer balloon temperature than fully opening both valves 136and 138. Pressure transducer PT5 may monitor the fluid recovery conduit48 pressure and transmit data to the operating console 14.

For any of the above embodiments, one or more temperature and/orpressure sensors 76 located in the balloon chamber 34 or any other pointwithin the system flow path 96 may transmit data to the operatingconsole 14, which information may be processed and displayed orotherwise communicated to the operator. Based on the transmitted and/orcommunicated data, one or more system parameters may be adjustedautomatically or semi-automatically by the one or more processors, ormanually by the operator. The one or more processors 58 may beprogrammed to execute one or more algorithms to communicate systemparameters to the operator and/or suggest automatic control tasks to theoperator, and/or automatically or semi-automatically control systemparameters (for example, open or close one or more valves, adjust theratio of liquid to gaseous refrigerant, and the like) to adjust thetemperature of the balloon 16 and, therefore, the effect the catheter 12has on target tissue. For example, if one or more temperature sensors,mapping electrodes, timers, or the like indicates to the one or moreprocessors 58 that the target tissue has been ablated, or the treatmenthas gone on for a predetermined amount of time, the one or moreprocessors 58 may automatically control one or more valves (such as toadjust the liquid to gaseous refrigerant, bypass the subcooler, and/orrestrict the fluid recovery conduit 48) to increase the temperature ofthe balloon 16 to a temperature within a range of between approximately−20° C. and approximately −25° C. in order to extend the thawing phaseof the treatment, which may result in more complete cell destruction andtherefore in a reduced likelihood of reconduction.

Any of the system components shown and described herein may be usedalone or in combination with any of the other system components shownand described herein in order to achieve a desired result. Further, thesystem components may be added to existing cryoablation systems toprovide a fully controllable balloon temperature.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

What is claimed is:
 1. A system for controllable adjustment of thetemperature of a treatment element of a medical device, the systemcomprising: a fluid delivery conduit including an upstream portion and adownstream portion; a subcooler located between the upstream fluid flowpath and the downstream fluid flow path; a bypass fluid flow path havinga first end that is in direct communication with the upstream fluid flowpath and a second end that is in direct communication with thedownstream fluid flow path; a first valve located in the upstream fluidflow path between the subcooler and the first end of the bypass fluidflow path; and a second valve located in the bypass fluid flow path. 2.The system of claim 1, further comprising a refrigerant source in fluidcommunication with the fluid delivery conduit.
 3. The system of claim 2,wherein the treatment element reaches a minimum treatment temperaturewhen the first valve is completely open and the second valve iscompletely closed.
 4. The system of claim 2, wherein the treatmentelement reaches a maximum treatment temperature when the first valve iscompletely closed and the second valve is completely open.
 5. The systemof claim 2, wherein the refrigerant source is a liquid refrigerantsource, the system further comprising a gaseous refrigerant source influid communication with the fluid delivery conduit.
 6. The system ofclaim 5, wherein adjusting the ratio of gaseous refrigerant to liquidrefrigerant selectively controls the temperature of the treatmentelement.
 7. The system of claim 6, wherein the liquid refrigerant sourceis a first tank and the gaseous refrigerant source is a second tank. 8.The system of claim 6, wherein the liquid refrigerant source and thegaseous refrigerant source are a common tank.
 9. The system of claim 8,wherein the common tank defines a fluid reservoir, the liquidrefrigerant source being at the bottom of the fluid reservoir and thegaseous refrigerant source being at the top of the fluid reservoir. 10.The system of claim 9, wherein the common tank includes a first valve influid communication with the liquid refrigerant source and a secondvalve in fluid communication with the gaseous refrigerant source,manipulation of at least one of the first and second valves adjustingthe ratio of gaseous refrigerant to liquid refrigerant.
 11. The systemof claim 10, wherein the tank further includes a dip stick incommunication with the first valve and extending into the liquidrefrigerant source.
 12. The system of claim 10, wherein the first andsecond valves are on the same end of the common tank.
 13. The system ofclaim 10, wherein the first and second valves are on opposite ends ofthe common tank.
 14. The system of claim 1, wherein the fluid deliveryconduit is in fluid communication with the treatment element, the systemfurther comprising: a fluid recovery conduit in fluid communication withthe treatment element; a first valve in the fluid recovery conduit; anda second valve in the fluid delivery conduit, independent manipulationof at least one of the first and second valves selectively controllingthe temperature of the treatment element.
 15. The system of claim 1,wherein the fluid delivery conduit is in fluid communication with thetreatment element, the system further comprising: a fluid recoveryconduit in fluid communication with the treatment element; and a valvein the fluid recovery conduit, manipulation of the valve selectivelycontrolling the temperature of the treatment element.
 16. The system ofclaim 1, wherein at least one of the first and second valves ismanipulated until the treatment element achieves a temperature ofbetween approximately −20° C. and approximately −25° C.
 17. A system foradjusting a treatment temperature of a cryoablation device, the systemcomprising: a refrigerant source; a fluid delivery conduit configured tobe in fluid communication with the refrigerant source and thecryoablation device; a fluid recovery conduit configured to be in fluidcommunication with the cryoablation device; and a heating element inthermal exchange with the fluid delivery conduit.
 18. The system ofclaim 17, wherein the heating element is a thermoelectric heater. 19.The system of claim 17, wherein the fluid recovery conduit includes aheating fluid flow path, at least a portion of the heating fluid flowpath being in thermal exchange with the fluid delivery conduit.
 20. Thesystem of claim 19, wherein the heating fluid flow path includes avalve, manipulation of the valve selectively affecting the temperatureof at least a portion of the cryoablation device.
 21. A system foradjusting a treatment temperature of a treatment element of acryoablation device, the system comprising: a fluid delivery conduitincluding an upstream portion and a downstream portion, the upstreamportion being in fluid communication with a refrigerant reservoir andthe downstream portion being in fluid communication with the treatmentelement; a subcooler located between the upstream fluid flow path andthe downstream fluid flow path; a bypass fluid flow path having a firstend that is in direct communication with the upstream fluid flow pathand a second end that is in direct communication with the downstreamfluid flow path; a first valve located in the upstream fluid flow pathbetween the subcooler and the first end of the bypass fluid flow path;and a second valve located in the bypass fluid flow path, therefrigerant reservoir containing both a refrigerant in a gaseous stateand a refrigerant in a liquid state, the refrigerant reservoir having athird valve for delivering the gaseous state refrigerant to the fluiddelivery conduit and a fourth valve for delivering the liquid staterefrigerant to the fluid delivery conduit, independent manipulation ofat least one of the first, second, third, and fourth valves controllingthe temperature of the treatment element.
 22. The system of claim 21,wherein at least one of the first, second, third, and fourth valves aremanipulated so that the treatment element achieves a temperature ofbetween approximately −20° C. and approximately −25° C.